690 



ANNUAL EEPORT SMITHSONIAN INSTITUTION, 192 8 



after century, thus putting it beyond reasonable doubt that only a 

 real identity can explain so considerable a number of similarities. 



A close study of the diagrams already published will soon show 

 that the possibility of mere accident must be ruled out. This re- 

 markable coincidence in such rapid variations at such considerable 

 distances, caused by simultaneous melting of ice, seems not to be 

 explicable in any other way than as being due to variations in the 

 amount of heat received from the sun. Thus we have to do with 

 nothing less than a gigantic self-registering thermograph, showing 

 the variations in the radiation from the sun. With respect to the 

 physics of the sun, it is of interest to note that there often exists an 

 observed biennial variation as well as the annual one, which is indi- 

 cated by the connection of the varve variation of the two hemis- 

 pheres so that the north and south summers with their closely cor- 

 responding varves [)oint to a natural thermal year. It is still unde- 



FiGUEB 2. — Diagrams for fixing tbe ice recession 



termined in which hemisphere that year begins. For the solution of 

 this question it is of interest that for some j-ears past, observations 

 have been made in Chile, on the solar radiation, for comparison with 

 those executed since 20 years ago on the sunny heights in the far 

 west of the United States.- Whatever may be the astronomic cause 

 of the annual solar variation, it seems likely that its beginning and 

 end are probably to be found somewhere between the northern and 

 southern summers, or not far from the equinoxes. When this has 

 been fully established, our annual mean temperature ought to be 

 calculated for the natural thermal year, which should give much 

 more characteristic results than those obtained from the basis of 

 the arbitrary calendar year. Nevertheless, though it be granted that 



2 The measurements here referred to by tlie author are those carried on hy the Smith- 

 sonian Astrophysical Observatory at Mount Wilson, Calif., and near Calama, Chile, 

 which have been described in Smithsonian reports for many years. 



